Plasma etching methods in which anisotropic etching is carried out in a targeted manner are known from the related art. In particular, German Published Patent Application No. 42 41 045 describes a method for anisotropic etching of silicon, in which etching and passivation steps are carried out separately in alternation (silicon trench etching). However, silicon is etchable with a more or less great anisotropy using a mixture of etching and passivation gases with the aid of continuous nonalternating plasma etching. In the trench etching process, a Teflon-type polymer, which functions to protect the Si side walls and is, in the plasma made of Cx(H)Fy-containing gases such as C4F8, C3F8, C2F6, CHF3, C2H2F2, for example, deposited on the substrate alternating between the SF6 etching steps. The Teflon-type polymer layer permits anisotropic plasma etching of silicon since it is removed only at locations at which the ion incidence from the plasma takes place perpendicularly onto the wafer surface, i.e., on the mask and at the base of the etching trenches. The polymer layer remains essentially preserved on the silicon side walls, where there is no ion incidence, and thus protects the silicon side wall. In trench etching, the Teflon-type polymer protective layer remains on the silicon side walls at the end of the trench etching process. Photoresists typically function as a mask material in trench etching, which are stripped off in commercial plasma strippers in an O2 plasma after the trench process.
Furthermore, plasma etching methods for structuring oxides or nitrides which are etched with the aid of Cx(H)Fy gases are known from the related art. Gases of this type have a more or less strong polymerizing effect, depending on the C:F ratio. The higher the C:F ratio, the greater the tendency to polymerization. An H content acts like an increase in C:F ratio. The result of these plasma etching processes may depend on the extent to which the polymer residues created by the plasma etching method remain behind and in particular may be removed from the substrate having the structured surface. In particular the methods known from the related art do not appear suitable for all geometric conditions because the reactive particles or wet etching solutions required for removal in the plasma may not be able to penetrate so deeply into the trench structures (at high aspect ratios or with narrow gaps) or into undercuts or caverns created during etching. Even in the case of a MEMS polymer sacrificial layer, which is known from the related art, penetration of the reactive particles or wet etching solution to remove same in narrow dimensions and with further underetching is increasingly difficult. In addition, the structured surfaces are often shaped in such a way that the areas of the substrate having the residues after plasma etching are inaccessible for an ion incidence and therefore removal is difficult or even prevented.